#include <iostream>
using namespace std;

int add(int a = 2, int b = 3)
{
    return a + b;
}

int main()
{
    int c = add();
    int d = add(10);
    int e = add(10, 20);

    cout << "c=" << c << endl;
    cout << "d=" << d << endl;
    cout << "e=" << e << endl;
    return 0;
}

/* 运行:
c=5
d=13
e=30

 */